Power Sensing - GE 889 Instruction Manual

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Power Sensing

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4–70
AUX. VT CONNECTION
Range: Van, Vbn, Vcn, Vab, Vbc, Vca, Vn
Default: Van
Select the voltage type corresponding to the one applied to the Aux VT relay terminals
from bank J2. Select Vn (neutral voltage), if the neutral voltage is applied to the relay
auxiliary VT.
AUX. VT SECONDARY
Range: 10.0 to 240.0 V in steps of 0.1 V
Default: 120.0 V
Select the output secondary voltage of the aux. VT connected to the aux. VT input from
bank J2.
AUX. VT RATIO
Range: 1.00 to 5000.00 in steps of 0.01
Default: 1.00
Select the aux. VT ratio to match the ratio of the VT connected to the aux. VT input from
bank J2.
The nominal PHASE VT SECONDARY and the AUX VT SECONDARY voltage settings are the
voltages across the phase VT terminals and the auxiliary VT terminals correspondingly
when nominal voltage is applied.
For example, on a system of 13.8kV nominal primary voltage, and a 14400:120 volt VT in a
Delta connection, the secondary voltage would be 115V, i.e. (13800/14400)*120. For a Wye
connection, the voltage value entered must be the phase to neutral voltage which would
be 115/√3 = 66.4 V.
On a 14.4 kV system with a Delta connection and a VT primary to secondary turns ratio of
14400:120, the voltage value entered would be 120 V, i.e. 14400/120.
The power computation in the 889 relay is performed using the voltage and current inputs
from the card inserted in slot J. In cases when the connected VTs and CTs have opposite
polarity, the power sensing menu provides for inverting the power measurement.
Path:
Setpoints > System > Power Sensing > Power 1(2)
PHASE CT&VT POLARITY
Range: Same, Inverse
Default: Same
When "Inverse" is selected, this setpoint inverts (multiplies phase currents by "-1" ) the CT
polarity for the phase currents from CT bank J1, with respect to the phase voltages from
the VT bank J2.
The setpoint for inversion of the power metering will be useful to avoid the physical
inversion of the CT connections on the relay. As the power metering will affect the power
directional elements, the user must determine the correct forward and reverse direction of
the power, before setup.
The selection of CT&VT polartiy for slot "K" is for future products.
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS